Your sensory perceptions (5 sense organs) are all outward bound. We can't scan internally with those 5 senses. We don't hear all the inner sounds of the body. You don't feel your blood pulsing. But you can feel a spider on your skin. These sensory organs deal with survival of the physical body.
But the inner sensory perception is a focus that must be honed. Turning inward is not a survival tool. It comes from our human nature to long to 'become more' and expand limitlessly, unlike any other creature.
No other creature wants to expand. They just want to have a full stomach.
Once our stomach is full we have 'many problems'... because of our human nature to expand beyond limitlessly.
So once we feel more settled about our survival needs, we turn to longing for expansion. Looking within is where we must go for this. But the mind's 'solutions' for both survival and expansion, is exactly what limits us - the mental striving tangles up this natural process of evolution and expansion. When we find more peace with Not Knowing, and have comfort with feeling Uncertain, we are in the ripe state of noticing inwardly without mental interruption or referencing to past.